The invention relates to a method of operating a tank device of a motor vehicle, wherein the tank device includes a tank and a tank ventilation device with at least one switching valve to which an excitation current can be applied, and the switching valve opens only when the excitation current exceeds an excitation current threshold over a certain period of time. The invention further relates to a tank device of a motor vehicle.
Methods of the afore-mentioned type are known in the art. The tank of the tank device may, for example, be a fuel tank or an auxiliary material tank, with the auxiliary material being in particular a reducing agent. The tank usually always contains a fluid, that is, for example, fuel or auxiliary material in liquid form, and possibly also in gaseous form. The gaseous fluid mixes hereby with air prevalent in the tank. In particular when filling a fluid into the tank, but also when the fluid contained in the tank expands due to a rise in temperature, pressure rises in the tank. In conventional motor vehicles, it is now common to ventilate the tank via a filter device. The filter device includes, for example a filter, in particular an activated carbon filter. The latter is regenerated from time to time, which means that fresh air is guided through the filter in a direction of a running internal combustion engine of the motor vehicle. With the aid of fresh air, fluid previously trapped in the filter is discharged, conducted in the direction of the internal combustion engine, and subsequently combusted in it.
This approach is not directly applicable in motor vehicles with hybrid drive devices, because the hybrid drive device has in addition to the internal combustion engine a further drive unit, and the internal combustion engine is oftentimes not operated for a long period of time. During this time period, purging of the activated carbon filter is not possible. For this reason, the tank can be formed as a so-called pressure tank to withstand an internal pressure which sometimes is significantly greater than the ambient pressure in the surroundings of the tank device. In addition, there is no permanent vent connection between the tank and the filter device but can be interrupted by a valve unit. This valve unit has the switching valve, for example a solenoid valve. Excitation current can be applied to the switching valve which opens however only when the excitation current exceeds the excitation current threshold. Excitation current or excitation current threshold may relate hereby to a current or a voltage.
Such a tank device can experience icing, particularly at low ambient temperatures. This is especially the case, when condensate has previously formed in the valve device or the switching valve. For example, moist air is drawn from the surroundings of the tank device, when the tank is vented via the vent connection or during regeneration. The contained moisture condenses in the valve device and freezes subsequently. As a result, the valve device or the solenoid valve can seize, so that the vent connection can no longer be established thereafter. Accordingly, the tank cannot or only insufficiently be aerated and/or vented, so that the pressure in the tank becomes impermissibly high or low and damage to the tank is the result.